The present invention relates to an organic-inorganic perovskite having alternating layers of an inorganic anion layer and an organic cation layer. More particularly, the present invention relates to an organic-inorganic perovskite in which the inorganic anion layer has a metal-deficient framework of corner-sharing metal halide octahedra and the organic cation layer has a plurality of organic cations capable of templating the inorganic anion layers within the perovskite structure.
The basic structural motif of the perovskite family is the ABX3 structure, which has a three-dimensional network of corner-sharing BX6 octahedra (FIG. 1a and FIG. 1b). The B component in the ABX3 structure is a metal cation that can adopt an octahedral coordination of X anions. The A cation is situated in the 12-fold coordinated holes between the BX6 octahedra and is most commonly inorganic. By replacing the inorganic A cation with an organic cation, an organic-inorganic hybrid perovskite can be formed.
In these ionic compounds, the organic component is an intimate part of the structure, since the structure actually depends on the organic cation for charge neutrality. Therefore, such compounds conform to specific stoichiometries. For example, if X is a monovalent anion such as a halide, and A is a monovalent cation, then B should be a divalent metal. Layered, two-dimensional A2BX4, ABX4 and one-dimensional A3BX5, A2Axe2x80x2BX5 perovskites also exist and are considered derivatives of the three-dimensional parent family.
The layered perovskites, for example, can be viewed as derivatives of the three-dimensional parent members, with y-layer-thick cuts, i.e., y=1, 2, 3 or more, from the three-dimensional structure interleaved with organic modulation layers. The layered compounds generally have inorganic layers with either  less than 100 greater than  or  less than 110 greater than  orientation relative to the original three-dimensional perovskite structure.
One  less than 100 greater than -oriented family of organic-inorganic perovskites has the general layered formula:
(R-NH3)2Ayxe2x88x921MyX3y+1
where M is a divalent metal, X is a halogen atom (i.e. Cl, Br, I), A is a small inorganic or organic cation (e.g. Cs+, CH3NH3+), R-NH3+ is a larger aliphatic or aromatic mono-ammonium cation, and y is an integer defining the thickness of the inorganic layers. In this system, the ammonium group is hydrogen-bonded to the inorganic sheet halogens, with the organic tail extending into the space between the layers and holding the structure together via Van der Waals interactions.
The (R-NH3)2MX4 (y=1) members of this family comprise the simplest and most numerous examples of organic-inorganic perovskites. Similar y=1 (or higher y) layered perovskite structures can also be stabilized by diammonium cations, yielding compounds with the general formula (NH3-R-NH3) MX4. In these systems, there is no Van der Waals gap between the layers since the ammonium groups of each organic layer hydrogen bond to two adjacent inorganic layers.
D. B. Mitzi, Prog. Inorg. Chem., 48, 1 (1999) reviews the state of the art and describes organic-inorganic perovskites that combine the useful properties of organic and inorganic materials within a single molecular-scale composite.
U.S Pat. No. 5,882,548 to Liang et al. describes solid state preparation of perovskites based on divalent metal halide sheets.
C. R. Kagan et al., Science, 286, 945 (1999) and copending U.S. Pat. Appl. Ser. No. 09/261,515,257/40 Filed Mar. 3, 1999 the contents of which are incorporated herein by reference, describe integrating the self-assembling nature of organic materials with the high carrier mobilities characteristic of inorganic materials for possible use in Organic-Inorganic Field-Effect Transistors (OIFET""s). A semiconductor-metal transition and high carrier mobility in the layered organic-inorganic perovskites based on a tin(II) iodide framework have also been described. These materials may be used as channel materials for field-effect transistors.
Copending U.S. Pat. Appl. Ser. No. 09/350,428, Filed Jul. 8, 1999, the contents of which are incorporated herein by reference, and D. B. Mitzi et al., Inorganic Chem., 38(26), 6246 (1999) describe combination of band gap tunability from the inorganic framework and high luminous efficiency from an organic dye component in single crystals and thin films of hybrid perovskites.
K. Chondroudis et al., Chem. Mater., 11, 3028 (1999) describe single crystals and thin films of the hybrid perovskites, which can be employed in Organic-Inorganic Light-Emitting Devices (OILED""s).
M. Era et al., Appl. Phys. Lett. 65, 676 (1994) and previously cited K. Chondroudis et al., Chem. Mater., 11, 3028 (1999) describe unique physical properties such as strong room temperature photoluminescence, third harmonic generation, and polariton absorption arising from excitons in the inorganic sheets. The excitons display large binding energies ( greater than 300 meV) and oscillator strength. The strong photoluminescence and the ability to tune the emission wavelength by means of incorporating different metal or halogen atoms in the structure make these perovskites attractive as emitter materials in electroluminescent devices. These materials may be used as channel materials for field-effect transistors.
Thus, despite the numerous examples of layered perovskites described above that are based on divalent metal halides and simple organic diammonium salts, there are no examples of layered organic-inorganic perovskite structures prepared from trivalent or higher valent metal halides combined with organic diammonium salts.
Furthermore, attempts to stabilize trivalent bismuth based layered perovskite structures with relatively short chain alkylammonium cations, which are known to stabilize layered perovskite frameworks based on divalent metal cations, have not been successful. Such attempts have resulted in entirely different structures as described by G. A. Mousdis et al., Z. Naturforsch., 53b, 927 (1998), wherein bismuth halide structures having one-dimensional zig-zag chains of corner-sharing BiX6 octahedra have been obtained.
Accordingly, it is an object of the present invention to provide novel semiconducting or insulating organic-inorganic hybrid perovskites that are based on metal-deficient inorganic frameworks.
It is another object of the present invention to provide low-cost, easily processed organic-inorganic perovskites, which can be used as materials in flat panel displays, non-linear optical/photoconductive devices, chemical sensors, emitting and charge transporting layers in organic-inorganic light-emitting diodes, organic-inorganic thin-film transistors and as channel layers in organic-inorganic field-effect transistors.
It is a further object of the present invention to provide simple and cost-effective methods of preparing the novel organic-inorganic perovskites.
These and other objects of the present invention will become apparent by the novel perovskite compositions and the methods of preparing the perovskite compositions.
The present invention includes an organic-inorganic perovskite, comprising alternating layers of:
an inorganic anion layer having a metal-deficient framework of corner-sharing metal halide octahedra, wherein the metal has a valence n of greater than 2, the metal halide layer being represented by the formula:
(Mn+)2/nV(nxe2x88x922)/nX42xe2x88x92
wherein M is a metal; V is a vacancy; X is a halide; and n is an integer greater than 2; and
an organic cation layer having a plurality of organic cations capable of templating the metal-deficient inorganic anion layers within the perovskite structure.
The present invention further includes a first method of preparing an organic-inorganic perovskite having alternating inorganic anion and organic cation layers, comprising the steps of: (a) contacting (i) a hydrogen halide salt of an organic diamine and (ii) a metal halide having a metal valence greater than 2, wherein the contacting is carried out in the presence of a solvent and hydrogen halide to produce a solution; and (b) supersaturating said solution to precipitate said perovskite. Preferably, the reaction mixture is supersaturated by cooling.
The present invention still further includes a second method of preparing an organic-inorganic perovskite having alternating inorganic anion and organic cation layers, comprising the step of: contacting (i) a hydrogen halide salt of an organic diamine and (ii) a metal halide having a metal valence greater than 2, wherein the contacting is carried out at a temperature and for a length of time sufficient to produce a perovskite.